Table 8. —Egg mortality caused by retention of eggs, Olsen Bay, 1961 



Date and area sample taken 



July-August 



West Fork weir 



East Fork weir 



Intertidal 



Total 



September 

 Intertidal 



Females 



Number 



97 



U7 

 100 



34A 



29 



Mideye to hypural plate. 

 2 Based on 2,094- eggs in complete ovaries. 



life was relatively brief for all spawners at 

 that time, as evidenced by recovery of tags 

 (fig. IZ). Most of the females that had retained 

 a high proportion of their eggs bore no visible 

 evidence of disease or bear wounds. Hunter 

 (1959) reported average egg retention ranged 

 fronn 0.1 to 2.7 percent for female pink salnnon 

 in Hook Nose Creek, British Columbia, and he 

 saw no evidence of increased egg retention 

 associated with high spawning densities. 

 Hanavan and Skud (1954) observed egg reten- 

 tion of to 51 percent for females confined 

 in pens, and retention was greater in the nnore 

 crowded pens. 



SURVIVAL OF EGGS AND LARVAE 



Sampling Procedure 



Egg densities in intertidal gravels were 

 deternnined with the aid of egg pumping equip- 

 ment and sampling procedures similar to those 

 desjcribed by McNeil.' Tidal strata were lo- 

 cated and defined as areas bounded by eleva- 

 tions above mean lower low tide. Sample plots 

 4 square feet in area were chosen at randonn 

 by the following procedure: Two randonn num- 

 bers were drawn, one for the linear distance 

 along the stream channel fronn a base point, 

 and the other for the distance from the left 

 bank measured perpendicularly to streamflow. 

 Sampling was continued in each stratum until 

 the variation of the mean number of pink 

 salmon eggs per plot was less than 20 percent 

 at the 90-percent confidence level, or when it 

 became apparent that further sampling would 

 result in little reduction in the variation. 

 Digging in each plot within a stratum was 



'William J. McNeil. A method of estimating total 

 mortality of pink salmon eggs and larvae. Unpublished 

 manuscript on file at the Bureau of Commercial Fisheries 

 Biological Laboratory, Auke Bay, Alaska. 



Length''' 



Cm. 



A6.3 



45.1 



54.7 



Eggs retEiined^ 

 per female (mean) 



Number 



56.4 



106.2 



64.1 



79.9 



849.5 



Egg mortality^ 



Percent 



2.7 

 5.1 

 3.1 



3.8 



41.5 



terminated only when negligible numbers of 

 eggs were displaced by repeated efforts. Pink 

 and chum salmon eggs were tabulated separa- 

 rately. Chum salmon eggs made up less than 10 

 percent of all eggs dug both years, and data 

 for them are not included in this report. 



Eggs or fry were dug in the autumn and 

 again in the spring at the 3- to 4-foot, 7- to 

 9-foot, and 10- to 1 1 -foot intertidal strata of 

 Olsen Creek each year. Additional samples 

 were dug from all strata between the 2- and 

 12-foot levels of the Little Creek area in 

 October 1960. The autumn egg samples were 

 taken soon after spawning was finished, 

 October 4 to 13, 1960, and September 28 to 

 October 4, 1961. This schedule allowed a 

 minimum time to elapse before eggs could 

 disappear because of predation or disintegra- 

 tion, but sufficient embryonic development 

 had occurred so that the difference between 

 live and dead eggs could be recognized. 



Egg Deposition 



The Olsen Creek, Little Creek, and Middle 

 Slough intertidal areas (fig. 1), measured from 

 the 3- to the 12-foot tide levels, had a total 

 low-flow stream bottom area of 243, 139 square 

 feet. It was estimated that the intertidal runs 

 comprised 41,580 females, with an average 

 egg content of 1,815 eggs per female in 1960 

 and 53,000 females with 2,094 eggs per female 

 in 1961. From this information it was calcu- 

 lated that potential egg deposition per square 

 foot was 300 in 1960 and 450 in 196l. 



Egg densities actually encountered in autumn 

 egg pump samples ranged from a mean nunn- 

 ber of 21 eggs per square foot at the 3- to 

 4-foot stratum in 1960, to 336 at the 10- to 

 11 -foot stratum in 1961 (table 9). 



Average egg deposition was slightly higher in 

 the 7- to 9-foot stratum (with densities of 213 to 

 285 per square foot) than in the 10- to 1 1 -foot 

 stratum (with densities of 151 to 336). At the 



21 



